Cement for holding diamonds during polishing



IINITEI) STATES PATENT OFFICE.

CLYDE J. COLEMAN, OF NEW ROCHELLE, NEW YORK, ASSIGNOR TO STERN-COLEMAN DIAMOND MACHINE COMPANY, INC., OF NEW YORK, N. Y.

CEMENT FOR HOLDING DIAMONDS DURING POLISHING.

No Drawing.

To all whom it may concern:

Be it known that I, CLYDE J. COLEMAN, a citizen of the United States, and a resident of Premium Point Park, New liochelle, county of Westchester, State of New York, have invented certain new and useful Im provements in Cement for Holding Diamonds During Polishing, of which the following is a specification.

This application is a continuation in part of my prior application, Ser. No. 808,280, filed December 22, 1913.

In polishing diamonds, it is the practice at the present time to hold the diamond in the polishing tool by partially embedding it in a body of metal in a semi-molten state, contained in a small brass basin or dop, the diamond being held in position by the metal after the metal has cooled. This method suffers from the disadvantage that it is necessary from time to time to soften the metal and readjust the diamond to expose a different part thereof for polishing, as it is not possible to expose at one time all parts of the diamond on one side of the girdle line. It is also common practice to lock the larger stones in a clamping device, but this device is very difficult to adjust so as to hold the diamond at the correct angle. The difficulty in holding diamonds during the polishing operation, as distinguished from other precious stones, is due to the extreme hardness of the diamond which necessitates applying great pressure, with resultant great friction and generation of great heat. Dia mond polishing is particularly a diflicult operation and unlike any other lapidary work because with all other gems there is something harder than they are, which will easily abrade them and not require any special speed or pressure to polish them, but the diamond being the hardest known substance, it must be polished with its own dust. This requires great lap speed, great pressure and also a precise grain presentation to the direction of movement of the lap, with the result that a high temperature is generated and often an almost instantaneous rise from low red heat to white red heat is developed when a hard spot is encountered and then dropping back suddenly to the normal red heat.

Th object of the invention is to provide a cement for holding diamonds in position during polishing, so as to avoid the disad- Specification of Letters Patent.

Patented Feb. 3, 1920.

Application filed January 25, 1916. Serial No. 74,076.

vantages of the prior methods, and in particular to make it possible to polish all faces of the diamond on one side of the girdle line without reclamping or'resetting the diamond in its holder, thereby avoiding the troublesome adjustments, calling for skilled manipulation, heretofore necessary. Such a cement must possess resistance against the disintegrating effect of great vibration, must be refractory enough to resist tlie heat of p0lishing, must be strong and adhesive to resist the pressure and strain and must have substantially the same coeflicient of expansion or a requisite degree of elasticity which is equivalent thereof, so that its adhesion will not be destroyed or impaired by expansion or contraction due to such temperature changes.

To these ends the invention contemplates a cement for attaching the diamond to the arbor by adhesive action, the cementhaving the physical characteristics that it does not disintegrate or soften under the heat of the polishing operation, and has a coeflicient of expansion so near that of the diamond or such a degree of elasticity that the diamond during the polishing may be rigidly held in place by the cement applied to the diamond on one side of the girdle, whereby substantially all the facets on one side of the girdle may be polished without resetting or reclamping the diamond to the arbor.

I find that a cement having clay as the principal base gives excellent results in such a method of securing the diamond to the arbor. With the clay base there is preferably employed a binder such as a compound in the nature of an enamel, preferably borax and nitrate of antimony. However, other binders or equivalent materials may be used to increase the adhesive properties of the cement. The cement also preferably contains graphite or its equivalent.

One method of compounding such a cement is as follows: Take 50 parts of bulk of Dixons stove polish (composed of clay and 40% graphite) ,selecting that which is dense hard and of good body and not friable, crumbly, sooty or of a dirty nature, and 50 parts by bulk of pure white soapstone clay, such as the talcum and steatite varieties, and 20 parts by bulk of borax or boric acid, and 10 parts by bulk of nitrate of lead, and with these in finely divided condition, mix them thoroughly, Nitrate of antimony is then prepared in the form of a concentrated solution, by allowing strong nitric 'acid to act on an excess of antimony for about ten to sixteen days. The powdered mixture is then made into a thick, creamy paste with a suflicient amount of the nitrate of antimony solution. This paste is allowed to stand for 24 hours or longer, and then it is made again into a similar paste with water.

Better results have been obtained by omitting the nitrate of lead and using the nitrate of antimony alone with the clay, graphite and boraX. Thus 32 parts by weight of the Dixons stove polish, 16 parts by weight of clay, and 152 parts by weight of boraX may be mixed with the nitrate of antimony solution as above described, except that it is preferable to dilute the nitrate of antimony solution with an equal amount of water before using it to make the paste. Obviously other materials than those mentioned may be used to miX with the clay to bring out its adhesive qualities, hence the invention is not limited to the precise materials and quantities named.

The paste is placed between the diamond and the arbor, preferably being applied in considerable body, so that it will be anchored in the arbor and will form a stem within the arbor for adhesively holding the diamond, and it is baked with the parts held together, at a high temperature, preferably in a nonoxidizing environment, as by inclosure in a retort containing carbon monoXid or nitrogen gas. The heat is first applied at a low temperature to dry the material and is gradually increased to 800 F. or higher. The temperature required will vary, however, depending upon the particular ingredients used and their proportions. The baking usually requires from 25 to 30 minutes. The cement is preferably gradually cooled.

While'I have described in detail certain formulae for a cement, which may be used for securing the diamonds for polishing, it will be understood that cements having different ingredients, but having the characteristics mentioned may well be used, as well as other cements containing the same materials, but in different quantities. Accordingly, my invention in its broader aspects is not limited to the details described. For eX- ample, graphite or other carbonaceous matter may be used instead of the DiXons stove polish. Other solutions or liquids may be used to make the paste and other materials substituted for the boraX or boron compound, or even for the clay base and some of the ingredients may be omitted.

Having fully and clearly described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The improved cement for holding diamonds during the polishing thereof, by adhesive action, which cement has the physical characteristic that it will rigidly hold the diamond during the polishing operation by adhesion thereto, and which contains clay as a principal base and a. binder formed of a combination containing nitrate of antimony and a oron compound.

2. The improved cement for holding diamonds during the polishing thereof, by adhesive action, which cement has the physical characteristic that it will rigidly hold the diamond during the polishing operation by adhesion thereto, and which contains clay as a principal base, a boron compound, and a binder formed of a solution containing a salt of antimony, in proportion such that upon baking the cement will rigidly hold the diamond.

3. The improved cement for holding diamonds during the polishing thereof, by adhesive action, which cement has the physical characteristic that it will rigidly hold the diamond during the polishing operation by adhesion thereto, and which contains clay as principal base and a boron compound and a binder containing salts of antimony and lead.

a. The improved cement for holding diamonds during polishing, by adhesive action, which cement has the physical characteristic that it will rigidly adhere to the diamond during polishing and which contains approximately 32 parts by weight of Dixons stove polish, 16 parts by weight of clay, 12 parts by weight of borax and sufficient solution of nitrate of antimony to form a paste thereof.

In testimony whereof, I have signed my name to this specification.

CLYDE J. CQLEMAN. 

